The use of copper alloys as wiring material substitutes for conventional aluminum alloys is advancing, with the aim of increasing the performance of LSIs. Copper alloys are poorly suitable for micromachining by dry etching which is often used for forming conventional aluminum alloy wiring. The “damascene method” has therefore been largely employed for micromachining of copper alloys, the method being one in which a thin-film of a copper alloy is accumulated on an insulating film having pre-formed trenches (recesses) and elevated sections (protrusions) to embed the copper alloy in the trenches, and then the copper alloy thin-film accumulated on the elevated sections (the copper alloy thin-film on sections other than the trenches) is removed by CMP to form embedded wiring (see Patent document 1 below, for example).
Chemical mechanical polishing (CMP) of metals such as copper alloys commonly involves attaching a pad (abrasive pad or abrasive cloth) onto a circular polishing plate (platen), wetting the pad surface with a polishing solution for metals, pressing the metal film-formed surface of a base substrate against the pad surface, rotating the polishing platen with a prescribed pressure (hereunder referred to as “polishing pressure”) being applied to the metal film from the back side of the base substrate, and removing the metal film on the elevated sections by mechanical friction between the polishing solution and the metal film on the elevated sections.
A polishing solution for metals to be used for CMP usually comprises an oxidizing agent and solid abrasive grains (hereunder referred to simply as “abrasive grain”), and it further comprises a metal oxide solubilizer, protective film-forming agent and the like if necessary. The basic mechanism of CMP employing a polishing solution comprising an oxidizing agent is considered to be that, first, the metal film surface is oxidized by the oxidizing agent to form an oxidation layer, and the metal film is polished by shaving the oxidation layer with the abrasive grain. In this polishing method, since the oxidation layer on the metal film surface embedded in the trenches of the insulating film is not significantly contacted with the pad and is not reached by the shaving effect of the abrasive grain, the metal film on the elevated sections is removed as CMP proceeds, thus flattening the substrate surface (see Non-patent document 1 below, for example).
For ordinary manufacturing of an LSI, the film thickness of the copper alloy thin-film to be polished is about 1 μm, and a polishing solution which allows a polishing rate of about 5000 Å/min is used (see Patent document 2 below, for example). In recent years, CMP treatment of copper alloys is being applied for manufacture of high performance microcircuit boards such as package boards, and also in the formation of Through Silicon Via (TSV) that have become an object of interest in new mounting methods.